1. Field of the Invention
This invention relates to a process for control of odor and septicity of sewage or wastewater by adding a source of sulfur dioxide to sewage or wastewater, sewage conduit, and sewage systems in the presence of metal catalyst(s). The invention also relates to a process for purification of sewage or wastewater by biological active substances after adding a source of sulfur dioxide therein. A source of sulfur dioxide is selected from the group consisting of sulfur dioxide, sulfite, bisulfite, metabisulfite, pyrosulfite, sulfurous acid, a solution of sulfur dioxide or sulfurous acid in sodium hydroxide or lime or any other alkali. Henceforth, "source of sulfur dioxide" or "sulfur dioxide species" or "active sulfur dioxide species" will be used for any one of the compounds: sulfur dioxide, sulfite, bisulfite, metabisulfite, pyrosulfite, sulfurous acid, a solution of sulfur dioxide in sodium hydroxide or in lime or in any other alkali, and a solution of sulfurous acid in sodium hydroxide or in lime or in any other alkali. The invention also prevents further formation of odoriferous compounds in sewage, and sulfide-induced corrosion.
The invention is particularly addressed to the problem of recovering sewage or wastewater from septicity. In the presence of a source of sulfur dioxide or mixtures thereof, the metabolic conditions of the microorganisms present in sewage or wastewater are modified and improved. In the presence of a source of sulfur dioxide, or mixtures thereof, the microorganisms regain their ability to absorb oxygen from the atmosphere or any other oxygen-containing source and ability to metabolize. The conditions and substances which are detrimental to microbial metabolism are reduced in the presence of active sulfur dioxide species. The seeds of biological active substances added to sewage or wastewater or the microorganisms already present therein, will rapidly remove nutrients from sewage or wastewater in the presence of a source of sulfur dioxide or mixtures thereof. Thus the invention is directed to initiation and promotion of biosynthesis by uptake of oxygen, and purification of sewage or wastewater by increasing the efficiency of the biological active substances.
2. Description of the Prior Art
The characteristics of sewage or wastewater is its highly disagreeable odor. Many organic and inorganic compounds contribute to the formation of this odor. But mostly inorganic and organic sulfur compounds are held responsible for the odor. The principal among the sulfur compounds is hydrogen sulfide. It is also easy to detect . When almost no hydrogen sulfide formation takes place in sewage or wastewater, it is considered as odorless. Therefore, hydrogen sulfide is taken as a representative of odor forming compounds. Hydrogen sulfide in sewage or wastewater creates a public nuisance because of its highly disagreeable odor at level as low as 0.01 parts per million (ppm) in the atmosphere. Breathing by humans of air containing as low as 10 ppm of hydrogen sulfide for a period of time can prove fatal; such accumulations are likely to occur in covered or doomed clarifiers or settling tanks in treatment plants, or in manholes or wet wells in sewerage systems. Besides odor, hydrogen sulfide formation results in heavy corrosion of metal and concrete sewer lines, concrete and metal structures, and metal equipment and machinery. The corrosion is greatly reduced when the formation of hydrogen sulfide can be reduced in sewage. So far it is known, the presence of hydrogen sulfide is also detrimental to the growth of the microorganisms and other biological active substances. The microorganisms and biological active substances can not properly metabolize in the presence of hydrogen sulfide . Thus the efficiency of purification of sewage or wastewater is decreased.
Hydrogen sulfide is also not easily oxidized. It can exist being supersaturated with oxygen in aqueous solution. The occurrence of hydrogen sulfide in the Baltic Sea, the North Sea, and the Atlantic Ocean supersaturated with oxygen has been reported (Leck, C. and Bagender, L. E., Anal. Chem., 1988, 1680-1683).
Although hydrogen sulfide is almost always formed in wastewater or sewage, sewage conduit, and sewage systems, the rate of formation is greatly enhanced in sunder temperature and prolonged anaerobic condition.
The conditions under which hydrogen sulfide is formed in sewage or wastewater is called septic. In fact, the microorganisms present therein turns black and seems lifeless or in serious metabolic disorder. Until this condition is reversed, sewage or wastewater can not be efficiently purified by biological active substances. Any seed of biological active substances added therein will not function, properly in septic condition and will fail to remove the nutrients properly from said sources. By adding a source of sulfur dioxide or mixtures thereof, the altered conditions of sewage or wastewater can be corrected.
Although, many treatments to control formation and regeneration of hydrogen sulfide in sewage or wastewater have been tried, none has been uniformly satisfactory or successful in both gravity systems and force main systems. Among those treatments used have been aeration, chlorination, ozonation, lime, sodium nitrate, activated carbon filtration, odor masking, hydrogen peroxide oxidation, and iron salts.
Ferric Chloride is widely used to control odor as well as for separation of phosphate in many treatment plants with moderate success. Many treatment plants in Europe and some in America have started to treat sewage or wastewater with pure oxygen. By treating with pure oxygen, the problem of odor, corrosion, and septicity have largely been overcome in sane treatment plants. But pure oxygen is not very satisfactory for controlling odor. One plant in Chicago which injects pure oxygen in the force main to control hydrogen sulfide, has to add hydrogen peroxide in the sun, her months in addition to pure oxygen to control hydrogen sulfide.
Pure oxygen is also expensive. It is not a cost-effective process for small plants. Many treatment plants in America are trying to explore some other alternative methods.
To evaluate the possibility of using alternative methods for controlling sewage odor, a literature search was conducted. Several patents were discovered which used sulfur dioxide or sulfurous acid for purification of sewage or wastewater in presence of iron and other metals preferably at a low pH. All the patents discuss methods for purification of water by chemical oxidation. No attempts have been made to purify sewage or wastewater by modifying or improving the biological process. No attempts have been made to purify sewage or wastewater by sulfur dioxide or sulfurous acid followed by biological active substances. None of these methods have been commercially accepted.
One example is U.S. Pat. No. 653,741 issued to Jewell in 1900, involves the use of sulfurous acid solution and scrap iron to produce a reactant solution that is mixed with water to be treated in a liquid process.
U.S. Pat. No. 2,171,203 to Urbain et al. teaches purification of organically polluted water such as sewage by generating Fe.sub.2 (SO.sub.4).sub.3 in situ by passing sulfur dioxide through a bed of scrap iron. The oxidizing power generated by this process is responsible for purification of sewage by chemical oxidation. U.S. Pat. No. 3,522,173 to Lindman et al. teaches the treatment of wastewater by the use of sulfur dioxide as an acidifying agent and iron as a flocculating agent to purify sewage or wastewater. However, the Lindman et al. process requires sulfur dioxide gas stream with large amounts of oxygen containing gases for the method to be effective. U.S. Pat. No. 3,948,774 issued Apr. 6, 1976 involves purification of water by treating wastewater with sulfur dioxide and iron between pH 2.4 and 2.6. Further, the use of sulfur dioxide for purification of wastewater is described in U.S. Pat. No. 4,123,355. In this process, sufficient sulfur dioxide is used to reduce the pH of the wastewater, generally in the order of 2 to 3.
Two patents to Maclachan, U.S. Pat. Nos. 511,418 and 1,543,939 each discuss the treatment of sewage sludge with sulfur dioxide gas. However, the patents make no mention of the process as being applicable to water treatment, and neither patent discuss the use of the method for water purification purposes.
Sulfur dioxide is also used as a disinfectant. U.S. Pat. Nos. 4,304,673 and 4,340,489 discuss processes by which wastewater is continuously disinfected by combining with wastewater with sufficient sulfur dioxide so that the wastewater has a selected free sulfur dioxide content of at least 5 mg/liter.
Cyanide can be almost completely oxidized by taking advantage of the oxidative power generated by sulfur dioxide oxidation. U.S. Pat. Nos. 4,537,686, and 4,615,873, and 4,622,149 claim that the cyanide content of industrial wastewater containing the same is removed by treatment with sulfur dioxide or an alkali or alkaline earth sulfite or bisulfite in the presence of excess oxygen and a metal catalyst which is, preferably, copper.
U.S. Pat. No. 2,87,177 issued Mar. 10, 1959 discusses a process of treating highly colored and odoriferous sulfur dyes waste liquors containing alkali metal sulfides with sulfurous acid and thereby converting them into a colorless and odorless liquid.
In all the patents, it appears that the oxidation of sulfur dioxide or other source of sulfur dioxide generate oxidizing power. The sewage and industrial waste has been purified by the oxidative power generated by the oxidation of sulfur dioxide and active sulfur dioxide species. By this way sewage and industrial waste has been purified chemically. But no attempt has been made to purify sewage and industrial waste by biological active substances after modifying and improving the condition of sewage with addition of a source of sulfur dioxide.
Recently, it has been claimed (Kotronarou et al., Research Journal, Wat. Env. Techn, 63(7) 1991, 965), that peroxymonosulfate is a more rapid and efficient oxidant of hydrogen sulfide and as a viable alternative to hydrogen peroxide for the control of sulfide-induced corrosion in concrete Sewer.
In mechanical treatment plants, wastewater is usually purified by activated sludge after some primary treatments. However, efforts are in progress to replace activated sludge by other biological active substances such as algea, and aquatic plants.
Research has been conducted for more than two decades on the use of water hyacinth, an aquatic plant, for treating domestic wastewater. Currently, at least five full scale water hyacinth systems are being used in the U.S. for removing nutrients--nitrogen and phosphorus from secondary effluents. Water hyacinth systems occupy more land than mechanical plants. As such have not been widely used. (DeBusk et al. J. Water Env. Techn. 61(7), 1989, p. 1217).
Smaller aquatic plants such as Duckweed, Pickerel Weed, Cattail, Bulrush, Elodea nuttallii have been proposed by many small communities for efficient purification of wastewater by natural process. However, further research are needed in order to find these plants useful in purification of wastewater (Buddhavarapu et al. Water Env. Techn., 3(3) 1991, 41; Bishop et al., J. Water Poll. Control. Fed. 61(5) 1989, 641; Zirschky et al. Water Env. Techn. 2(8) 1990, 37).
Algae known as activated algae or algal turf has been regarded as one of the most promising process in removing the nutrients from wastewater. Its use in wastewater treatment is a significant development, but it has not been fully explored (Maity et al. J. Water Poll. Control Fed. 60(10), 1988, 2115).
Algal turf has been found useful in purification of water in lagoons, and reefs. U.S. Pat. No. 4,333,263, on algal turf, has been issued to Walter Adey . These group of workers are trying to apply their method in purification of wastewater. Further research and development are needed in order to make activated algae or algal turf useful in purification of sewage or wastewater.
In order to understand the condition of sewage when it is confined in sewage conduit for a long time in the absence of oxygen and at high temperature, a study was made in the laboratory with said source of sulfur dioxide and activated sludge. During the course of the study, said source of sulfur dioxide were added together with metal salts to odoriferous black septic activated sludge. The black color of the activated sludge gradually turned gray and odor greatly reduced. The gray activated sludge turns black when it was allowed to sit in the laboratory in the absence of oxygen and gradually it becomes an increasing source of odor formation. However, on addition of said source of sulfur dioxide and iron salts, the black sludge again regain their gray healthy look and odor was also reduced. Thus it appeared that said source of sulfur dioxide could prevent activated sludge from being septic and essential for the metabolism of the activated sludge.
It is also believed that sulfur in the form of sulfite enters in biological reaction. Thus it appeared that sulfite and other source of sulfur dioxide have great potential in controlling sewage odor, recovering sewage from septicity, modifying the altered biological condition, increasing oxygen uptake in sewage, and promoting microbial metabolism, but said source of sulfur dioxide had never been used as such.
The problem of controlling sewage odor and purification of sewage in a cost-effective way by improving and modifying biological process, has basically not been solved.
It is, therefore, an object of the present invention to provide a process for the elimination of odor in wastewater or sewage, sewage conduit, and sewage systems by aerating and sulfur dioxide-sodium hydroxide treatment in the presence of metal catalysts. Instead of sulfur dioxide-sodium hydroxide solution, sulfite, bisulfite, metabisulfite, or pyrosulfite salts, preferably, alkali metal or alkaline earth metal salts, sulfur dioxide gas, a solution of sulfur dioxide in water, or sulfurous acid as well as mixtures of the various sulfur dioxide sources can be used. The source of sulfur dioxide can be added directly to the sewage or wastewater being treated. In the alternative, the source of sulfur dioxide can be first dissolved in water or in an alkaline solution, such as sodium hydroxide or lime, prior to be added to the sewage or wastewater.
Metal salts such as iron, copper, nickel, manganese, chromium, titanium, vanadium, and any other metals and compounds such as zinc, platinum, peroxydisulfate, peroxydiphosphate, and the like which promotes oxidation of sulfur dioxide or said sulfur dioxide species may be used.
It is a particular object of the present invention to provide a process for the recovery of sewage or wastewater from septicity, increase uptake rate of oxygen therein, and purify sewage or wastewater by initiating and promoting metabolism of biological active substances. It is also an object of the present invention to utilize oxygen injected in the form of any oxygen containing gas in sewage or wastewater and activated biological reactors as fully as possible by increasing oxygen absorbing capacity of said sources and thereby reducing the cost of the operation.
It is also an object of the invention to provide a process by which sulfide-induced corrosion of sewage treatment plants can be overcome.